News Article | May 3, 2017
In December 2016, NASA began accepting bids for its next New Frontiers competition, a chance to mount a $1 billion mission to solar system destinations such as the moon, Venus, or Saturn's moon Titan. It is a careermaking opportunity, and scientists devoured the rules in the announcement. In the second paragraph, they read something new: a sentence stating that "NASA recognizes and supports the benefits of having diverse and inclusive" communities and "fully expects that such values will be reflected in the composition of all proposal teams." Many scientists hope the language will help NASA get out of a rut. Over the past 15 years, women have made up just 15% of planetary mission science teams, even though at least a quarter of planetary scientists are women. The disparity is even worse for ethnic minorities: Blacks and Hispanics make up 13% and 16% of the country, respectively, but each group makes up just 1% of the nation's planetary scientists. (Firm numbers for specific missions are not available.) The New Frontiers deadline arrived last week, and although the proposals are not public, observers say that women lead at least four of the dozen or so NASA received. "I suspect teams that come in will be significantly more diverse than previous rounds," says Louise Prockter, director of the Lunar and Planetary Institute in Houston, Texas. NASA's move was spurred by scientists like Julie Rathbun, an expert on jovian moons at the Planetary Science Institute in Claremont, California, who has tried to quantify NASA's diversity problem. She and her peers dug up press releases and records to count the women on 26 missions. The lack of women on the 78-person science team for the Viking probes, sent to Mars in 1975, may not have been so surprising. But Rathbun expected women to be better represented on a newer generation of missions, and she was shocked to see no improvement in the past 15 years. "It hasn't happened yet," she says. Rathbun presented her analysis at meetings over the past 2 years, and the message eventually reached Curt Niebur, NASA's program scientist for New Frontiers in Washington, D.C. He says that pushing for more diversity is in NASA's interest. "The research now shows the best teams are those that take advantage of the diverse skills, knowledge, and viewpoints that are available," he says. Planetary science is not unique in its diversity problem. Many scientific disciplines, even those fed by academic pipelines that are majority female, such as biology, still have a disproportionate number of men in leadership roles. Janet Vertesi, a sociologist at Princeton University who studies planetary missions, says researchers have found that female and minority scientists can suffer even in the absence of conscious bias from majority scientists. Through the Matilda effect, for example, readers tend to assign more credit to male co-authors than female ones. And when minorities of any sort make up less than a third of a team, they face pressure to show that they were not selected because of their identity, which can cause conflicts. Some defenders of the status quo have claimed that it simply reflects merit. But Vertesi says that, without explicit criteria for "merit," people look for candidates from their existing social networks and exclude outsiders. As a federal agency, NASA won't impose sex- or race-based quotas in judging the New Frontiers proposals. And including demographic information on the mission proposals is still technically optional. But the change in the application language is a start, says Maria Zuber, vice president for research at the Massachusetts Institute of Technology in Cambridge, and the first woman to be a principal investigator for a NASA planetary mission. "If NASA gives it sufficient airplay, I think it will at least make people think." When it comes time to evaluate the mission proposals, Niebur says, he will require review panelists to perform exercises to raise awareness of unconscious biases they may have. NASA can take other tangible steps to boost diversity. For example, the agency has provided money to add outside scientists to many in-progress missions, a move meant to add new expertise to their research teams. Such participating scientist programs, as they're known, tend to improve diversity as well, according to a report from NASA's scientific advisory groups that was led by Prockter and released this week. She says she thinks that such programs should be mandatory for every mission. Other glimmers of progress are evident. Two years ago, women led four of the five proposals that were finalists in the competition for Discovery—a NASA line of missions with a $450 million limit. One of the two winners was led by Lindy Elkins-Tanton, a planetary scientist at Arizona State University in Tempe who, with her mission to a metallic asteroid, has now become the second woman to lead a competitive planetary science mission. Elkins-Tanton supports the new language, which could push the field one step closer toward a culture where all good ideas are heard. "We're trying to make it a meritocracy," she says.
Boyce J.W.,University of California at Los Angeles |
Tomlinson S.M.,University of California at Los Angeles |
McCubbin F.M.,University of New Mexico |
Greenwood J.P.,Wesleyan University |
Treiman A.H.,Lunar and Planetary Institute
Science | Year: 2014
Recent discoveries of water-rich lunar apatite are more consistent with the hydrous magmas of Earth than the otherwise volatile-depleted rocks of the Moon. Paradoxically, this requires H-rich minerals to form in rocks that are otherwise nearly anhydrous. We modeled existing data from the literature, finding that nominally anhydrous minerals do not sufficiently fractionate H from F and Cl to generate H-rich apatite. Hydrous apatites are explained as the products of apatite-induced low magmatic fluorine, which increases the H/F ratio in melt and apatite. Mare basalts may contain hydrogen-rich apatite, but lunar magmas were most likely poor in hydrogen, in agreement with the volatile depletion that is both observed in lunar rocks and required for canonical giant-impact models of the formation of the Moon.
Visscher C.,Lunar and Planetary Institute |
Moses J.I.,Space Science Institute
Astrophysical Journal | Year: 2011
We explore CO →↔ CH4 quench kinetics in the atmospheres of substellar objects using updated timescale arguments, as suggested by a thermochemical kinetics and diffusionmodel that transitions from the thermochemical-equilibrium regime in the deep atmosphere to a quench-chemical regime at higher altitudes. More specifically, we examine CO quench chemistry on the T dwarf Gliese 229B and CH4 quench chemistry on the hot-Jupiter HD 189733b. We describe a method for correctly calculating reverse rate coefficients for chemical reactions, discuss the predominant pathways for CO →↔ CH4 interconversion as indicated by the model, and demonstrate that a simple timescale approach can be used to accurately describe the behavior of quenched species when updated reaction kinetics and mixing-length-scale assumptions are used. Proper treatment of quench kinetics has important implications for estimates of molecular abundances and/or vertical mixing rates in the atmospheres of substellar objects. Our model results indicate significantly higher Kzz values than previously estimated near the CO quench level on Gliese 229B, whereas current-model-data comparisons using CH4 permit a wide range of Kzz values on HD 189733b. We also use updated reaction kinetics to revise previous estimates of the Jovian water abundance, based upon the observed abundance and chemical behavior of carbon monoxide. The CO chemical/observational constraint, along with Galileo entry probe data, suggests a water abundance of approximately 0.51-2.6× solar (for a solar value of H2O/H2 = 9.61 × 10-4) in Jupiter's troposphere, assuming vertical mixing from the deep atmosphere is the only source of tropospheric CO. © 2011. The American Astronomical Society. All rights reserved.
News Article | February 15, 2017
We can’t recreate the giant impact that led to the moon’s formation in a lab, but humans have made some other big explosions. By examining residue from the first detonation of a nuclear weapon, researchers have cracked a window into the moon’s past. On 16 July 1945, the US army detonated a nuclear weapon for the first time in an operation codenamed Trinity (see photo, above). As the bomb exploded with an energy equivalent to 20 kilotonnes of TNT, the sand underneath it melted, producing a thin sheet of mostly green glass dubbed trinitite. The explosion brought the area around the bomb to temperatures over 8000°C and pressures nearing 80,000 atmospheres. These extreme conditions are similar to those created as the moon formed in a colossal collision between Earth and another rock, probably about the size of Mars. “It is as close as we can probably get to conditions that you might envisage on a planetary body in the early solar system,” says James Day at the Scripps Institution of Oceanography in California. Fortunately for planetary science, scientists meticulously measured and recorded the details of the Trinity detonation, so there is plenty of information to work with. Day and his colleagues took advantage of that past precision to investigate why the moon has surprisingly little water and other volatiles with a relatively low boiling point – much less than Earth. To do so, they studied the distribution of one volatile element, zinc, in trinitite collected at different distances out from the explosion’s centre. They found that the closer to the explosion the trinitite formed, the less zinc it had, especially when it came to zinc’s lighter isotopes. That’s because these evaporated in the intense heat of the explosion, while the heavier isotopes didn’t and so remained in the trinitite. The ratios of different forms of zinc left behind in trinitite showed remarkable parallels to what was observed in the moon rocks retrieved in the Apollo missions. “What’s critical here is that the fractionation factors – how the heavy and light isotopes separate from each other – exactly match,” says Day. This means that zinc and other volatile elements, most notably water, probably evaporated off the moon while it was being formed in a violent collision or soon afterward, while its surface was still incredibly hot. Previously, glass deposits from the moon with unusually high amounts of volatiles had led scientists to suspect that the moon’s interior might have lots of water, similar to Earth’s mantle. This study casts doubt on that idea; if water evaporated along with other volatiles as the moon was being formed, it’s hard to imagine how much more could have lingered under the surface. “I think it’s a pretty neat use of some of the data that we have on the ground here on Earth to address a planetary problem,” says Patrick McGovern at the Lunar and Planetary Institute in Texas.
Kiefer W.S.,Lunar and Planetary Institute
Journal of Geophysical Research E: Planets | Year: 2013
The Marius Hills, the Moon's largest volcanic dome field, has more than 250 basaltic domes and cones in an area 200 × 250 km across. It is a major free-air gravity anomaly, 236 mGal in the north and 150 mGal in the south. In the northern half of the structure, the topography can only explain about half of the gravity anomaly, and in the south, there is virtually no topographic relief associated with the gravity anomaly. High-density material must be present at depth, most likely as mare basalt intruded into the underlying porous feldspathic highland crust. The gravity anomaly is modeled using two spherical caps. The northern cap is 160-180 km in diameter and at least 3.0 km thick. The southern cap is 100-140 km in diameter and at least 6.2 km thick. The intruded basalt may have served as the magma chambers that fed the overlying surface volcanism. Magma crystallization within these chambers provided a source of crystal-rich, high viscosity lava that fed the volcanic domes. The volume of intruded basalt is 1.6 × 104 km3. The total volcanic volume, including both intruded and extruded material, is 2.6 × 10 4 km3, indicating that the Marius Hills is a major volcanic center. Intrusion of hot magma may cause thermal annealing of the porous feldspathic host rock, significantly reducing the host rock porosity. This would allow a large volume of magma to be intruded into the crust with little change in overall crustal volume. © 2012. American Geophysical Union. All Rights Reserved.
Norman M.D.,Lunar and Planetary Institute |
Norman M.D.,Australian National University |
Nemchin A.A.,Curtin University Australia
Earth and Planetary Science Letters | Year: 2014
A sharp rise in the flux of asteroid-size bodies traversing the inner Solar System at 3.9 Ga has become a central tenet of recent models describing planetary dynamics and the potential habitability of early terrestrial environments. The prevalence of ~3.9Ga crystallization ages for lunar impact-melt breccias and U-Pb isotopic compositions of lunar crustal rocks provide the primary evidence for a short-lived, cataclysmic episode of late heavy bombardment at that time. Here we report U-Pb isotopic compositions of zirconolite and apatite in coarse-grained lunar melt rock 67955, measured by ion microprobe, that date a basin-scale impact melting event on the Moon at 4.22 ± 0.01Ga followed by entrainment within lower grade ejecta from a younger basin approximately 300 million yr later. Significant impacts prior to 3.9 Ga are also recorded by lunar zircons although the magnitudes of those events are difficult to establish. Other isotopic evidence such as 40Ar-39Ar ages of granulitic lunar breccias, regolith fragments, and clasts extracted from fragmental breccias, and Re-Os isotopic compositions of lunar metal is also suggestive of impact-related thermal events in the lunar crust during the period 4.1-4.3 Ga. We conclude that numerous large impactors hit the Moon prior to the canonical 3.9 Ga cataclysm, that some of those pre-cataclysm impacts were similar in size to the younger lunar basins, and that the oldest preserved lunar basins are likely to be significantly older than 3.9 Ga. This provides sample-based support for dynamical models capable of producing older basins on the Moon and discrete populations of impactors. An extended period of basin formation implies a less intense cataclysm at 3.9 Ga, and therefore a better opportunity for preservation of early habitable niches and Hadean crust on the Earth. A diminished cataclysm at 3.9 Ga suggests that the similarity in the age of the oldest terrestrial continental crust with the canonical lunar cataclysm is likely to be coincidental with no genetic significance. © 2013 Elsevier B.V.
Kiefer W.S.,Lunar and Planetary Institute
Planetary and Space Science | Year: 2012
Reliable measurements of the Moons global heat flow would serve as an important diagnostic test for models of lunar thermal evolution and would also help to constrain the Moons bulk abundance of radioactive elements and its differentiation history. The two existing measurements of lunar heat flow are unlikely to be representative of the global heat flow. For these reasons, obtaining additional heat flow measurements has been recognized as a high priority lunar science objective. In making such measurements, it is essential that the design and deployment of the heat flow probe and of the parent spacecraft do not inadvertently modify the near-surface thermal structure of the lunar regolith and thus perturb the measured heat flow. One type of spacecraft-related perturbation is the shadow cast by the spacecraft and by thermal blankets on some instruments. The thermal effects of these shadows propagate by conduction both downward and outward from the spacecraft into the lunar regolith. Shadows cast by the spacecraft superstructure move over the surface with time and only perturb the regolith temperature in the upper 0.8 m. Permanent shadows, such as from thermal blankets covering a seismometer or other instruments, can modify the temperature to greater depth. Finite element simulations using measured values of the thermal diffusivity of lunar regolith show that the limiting factor for temperature perturbations is the need to measure the annual thermal wave for 2 or more years to measure the thermal diffusivity. The error induced by permanent spacecraft thermal shadows can be kept below 8% of the annual wave amplitude at 1 m depth if the heat flow probe is deployed at least 2.5 m away from any permanent spacecraft shadow. Deploying the heat flow probe 2 m from permanent shadows permits measuring the annual thermal wave for only one year and should be considered the science floor for a heat flow experiment on the Moon. One way to meet this separation requirement would be to deploy the heat flow and seismology experiments on opposite sides of the spacecraft. This result should be incorporated in the design of future lunar geophysics spacecraft experiments. Differences in the thermal environments of the Moon and Mars result in less restrictive separation requirements for heat flow experiments on Mars. © 2011 Elsevier Ltd. All rights reserved.
Hurwitz D.M.,Lunar and Planetary Institute |
Kring D.A.,Lunar and Planetary Institute
Journal of Geophysical Research E: Planets | Year: 2014
We modeled the differentiation of the South Pole-Aitken (SPA) impact melt sheet to determine whether noritic lithologies observed within SPA formed as a result of the impact. Results indicate differentiation of SPA impact melt can produce noritic layers that may accommodate observed surface compositions but only in specific scenarios. One of nine modeled impact melt compositions yielded layers of noritic materials that account for observations of noritic lithologies at depths of ∼6 km. In this scenario, impact occurred before a hypothesized lunar magma ocean cumulate overturn. The 50 km deep melt sheet would have formed an insulating quenched layer at the surface before differentiating. The uppermost differentiated layers in this scenario have FeO and TiO2 contents consistent with orbital observations if they were subsequently mixed with the uppermost quenched melt layer and with less FeO- and TiO2-enriched materials such as ejecta emplaced during younger impacts. These results verify that noritic lithologies observed within SPA could have formed as a direct result of the impact. Therefore, locations within SPA that contain noritic materials represent potential destinations for collecting samples that can be analyzed to determine the age of the SPA impact. Potential destinations include central peaks of Bhabha, Bose, Finsen, and Antoniadi craters, as well as walls of Leibnitz and Schrödinger basins. Additionally, potential remnants of the uppermost quenched melt may be preserved in gabbroic material exposed in "Mafic Mound." Exploring and sampling these locations can constrain the absolute age of SPA, a task that ranks among the highest priorities in lunar science. Key Points SPA impact melt differentiation accommodates observed noritic surface materials SPA formed before LMO overturn to produce noritic material at the lunar surface Norite-bearing materials represent key samples for dating the age of SPA ©2014. American Geophysical Union. All Rights Reserved.
Bogard D.D.,Lunar and Planetary Institute
Chemie der Erde - Geochemistry | Year: 2011
Whereas most radiometric chronometers give formation ages of individual meteorites >4.5Ga ago, the K-Ar chronometer rarely gives times of meteorite formation. Instead, K-Ar ages obtained by the 39Ar-40Ar technique span the entire age of the solar system and typically measure the diverse thermal histories of meteorites or their parent objects, as produced by internal parent body metamorphism or impact heating. This paper briefly explains the Ar-Ar dating technique. It then reviews Ar-Ar ages of several different types of meteorites, representing at least 16 different parent bodies, and discusses the likely thermal histories these ages represent. Ar-Ar ages of ordinary (H, L, and LL) chondrites, R chondrites, and enstatite meteorites yield cooling times following internal parent body metamorphism extending over ~200Ma after parent body formation, consistent with parent bodies of ~100km diameter. For a suite of H-chondrites, Ar-Ar and U-Pb ages anti-correlate with the degree of metamorphism, consistent with increasing metamorphic temperatures and longer cooling times at greater depths within the parent body. In contrast, acapulcoites-lodranites, although metamorphosed to higher temperatures than chondrites, give Ar-Ar ages which cluster tightly at ~4.51Ga. Ar-Ar ages of silicate from IAB iron meteorites give a continual distribution across ~4.53-4.32Ga, whereas silicate from IIE iron meteorites give Ar-Ar ages of either ~4.5Ga or ~3.7Ga. Both of these parent bodies suffered early, intense collisional heating and mixing. Comparison of Ar-Ar and I-Xe ages for silicate from three other iron meteorites also suggests very early collisional heating and mixing. Most mesosiderites show Ar-Ar ages of ~3.9Ga, and their significantly sloped age spectra and Ar diffusion properties, as well as Ni diffusion profiles in metal, indicate very deep burial after collisional mixing and cooling at a very slow rate of ~0.2°C/Ma. Ar-Ar ages of a large number of brecciated eucrites range over ~3.4-4.1Ga, similar to ages of many lunar highland rocks. These ages on both bodies were reset by large impact heating events, possibly initiated by movements of the giant planets. Many impact-heated chondrites show impact-reset Ar-Ar ages of either >3.5Ga or <1.0Ga, and generally only chondrites show these younger ages. The younger ages may represent orbital evolution times in the asteroid belt prior to ejection into Earth-crossing orbits. Among martian meteorites, Ar-Ar ages of nakhlites are similar to ages obtained from other radiometric chronometers, but apparent Ar-Ar ages of younger shergottites are almost always older than igneous crystallization ages, because of the presence of excess (parentless) 40Ar. This excess 40Ar derives from shock-implanted martian atmosphere or from radiogenic 40Ar inherited from the melt. Differences between meteorite ages obtained from other chronometers (e.g., I-Xe and U-Pb) and the oldest measured Ar-Ar ages are consistent with previous suggestions that the 40K decay parameters in common use are incorrect and that the K-Ar age of a 4500Ma meteorite should be possibly increased, but by no more than ~20Ma. © 2011 Elsevier GmbH.
News Article | January 14, 2016
Ceres, the dwarf planet whose mysterious bright spots have held the public's attention, is revealing some of its secrets in the most recent images from NASA's Dawn spacecraft. The space agency has released dramatic new images, captured as the Dawn probe made its closest orbit above the surface of Ceres, passing over it as just 240 miles away. Taken during four days in December, the images highlight the Kupalo Crater, one of the tiny world's youngest. Bright material exposed on the crater's rim could be salt, and could be related to the "bright spots" seen in earlier images of Ceres, which researchers suspect are large salt deposits. "This crater and its recently-formed deposits will be a prime target of study for the team as Dawn continues to explore Ceres in its final mapping phase," says mission science team member Paul Schenk at the Lunar and Planetary Institute in Houston. Another crater featured in the new images, Dantu Crater, shows fractures on its 78-mile-wide floor, similar to what are seen on our moon in the large young crater known as Tycho, researchers noted. The cracking may be the result of cooling of materials melted by the impact, or the crater floor may have experienced uplifting after the forming of the crater, they suggest. The Dawn spacecraft launched in 2007, headed to two solar system targets: Vesta and Ceres, to two larger objects orbiting in the asteroid belt that lie between Mars and Jupiter. The probe arrived at Vesta in July 2011 and spent 17 months studying that tiny world before heading off to Ceres, arriving in orbit there in March 2015. While Ceres, with a diameter of around 587 miles, is considered a dwarf planet, scientists classify the slightly smaller 326-mile-wide Vesta as an asteroid. One of the goals of the Dawn mission was to contrast and compare the two bodies to gain an understanding of how they may have formed, NASA said in a statement. To that end, other instruments on the spacecraft have been busy analyzing the various wavelengths of light reflecting off of Ceres, which can help identify minerals on its surface. "When we set sail for Ceres upon completing our Vesta exploration, we expected to be surprised by what we found on our next stop," says mission principle investigator Chris Russell. The dwarf planet did not disappoint, he says. "Everywhere we look in these new low-altitude observations, we see amazing landforms that speak to the unique character of this most amazing world," says Russell, based at UCLA.